Localized Electron Magnetism in the Icosahedral Au–Al–Tm Quasicrystal and Crystalline Approximant

We report the magnetic, thermal, and transport properties of the Au–Al–Tm quasicrystal, which is isostructural to the first and only quasicrystal Au–Al–Yb that shows a novel quantum critical behavior. The Tm-based quasicrystal undergoes a spin-glass-like freezing below Tf ∼ 0.4 K. We also synthesize the Au–Al–Tm approximant to the quasicrystal and find that it shows a similar spin-glass-like freezing below Tf ∼ 0.3 K. Both the quasicrystal and the approximant follow the Curie–Weiss law in a wide temperature range above Tf, indicating that the 4f electrons are well localized on the vertices of the icosahedron. The interspin interaction is antiferromagnetic and its magnitude is as small as ∼1 K. The spin-glass-like freezing is presumably driven by the combined effect of the chemical disorder of Au/Al ions and the frustrated nature of the icosahedron. On the basis of these results, we discuss a possible origin of the unusual quantum criticality observed in the Yb-based system.